would the jetting on a 300ex carb be the same as the jetting of a 400ex carb on a 300ex?

 

No not really....you would start with that though. You will most likely have to tweek the needle and the air screw for sure - but start witht he 300ex hjets first, unless you find someone who has done the conversion and can give you specs.

 

one of my buddies thought those specs i gave you would be good. he is currently running that carb on a 250X. he said he would try a 145 keihin mainjet.